Projection apparatus, method of controlling projection apparatus, and projection system

ABSTRACT

Each projection apparatus in a multi-projection system has a liquid crystal panel, a driving circuit configured to perform PWM control of the liquid crystal panel, and a projection image processing unit configured to perform edge blending processing to perform compositing display by each projection apparatus and processing to change gain properties of the edge blending processing by each projection apparatus. Synchronization of each projection apparatus is maintained by a synchronization circuit. Therefore, a sum of image gain in a region of image compositing by each projection apparatus is 1, and the position and image gain properties of the compositing region are changed for each frame, so the position of image deterioration changes for each frame.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a projection apparatus, a method ofcontrolling the projection apparatus, and a projection system employinga plurality of projection apparatuses.

Description of the Related Art

There are projection apparatuses that form an image on a light valve ofa liquid crystal panel or the like, and display the image in anoptically enlarged projection. Recently, the resolution of video sourceshas increased, and it is desired to display images having a large numberof pixels, such as 4K2K or 8K4K images for example, on a large screen.Commonly, in order to increase the number of pixels and increase thescreen size of a projector, it is necessary to miniaturize light valvesof a liquid crystal panel or the like, and adopt a high-brightness lightsource, so cost increases. Therefore, many-pixel, large-screenprojection display is often performed by multi-projection using aplurality of inexpensive projectors having a conventional light valveand light source. Multi-projection is a method of arranging projectionscreens to be projected by a plurality of projection apparatuses in atile shape, and displaying one image as a whole. In the case ofmulti-projection, a process called “edge blending” is used that enablesthe joint between projection screens projected by each projectingapparatus to be inconspicuous. Edge blending is processing in which aportion of adjacent images of each projection screen are overlapped, andin order to maintain uniform illuminance within the projection screens,such that the total illuminance of the overlapped portion where aplurality of projection screens have been overlapped is equal to theilluminance of a non-overlapped portion, light reduction processing(referred to below as “gradation processing”) is performed on theoverlapped portion.

On the other hand, as a problem characteristic of liquid crystal panels,there is alignment abnormality due to a horizontal electric field fromadjacent pixels (referred to below as “disclination”). This is not aproblem limited to a PWM driving scheme, but is a phenomenon expressedby the amount of light emitted from a target pixel decreasing due tobeing affected by the horizontal electric field of the adjacent pixel,so that the amount of light emitted from the target pixel is less thanthe gradation originally desired to be displayed. In an analog drivingscheme in which video is expressed by applying a voltage proportional toa gradation value to liquid crystal, as a gradation difference between atarget pixel and an adjacent pixel increases, an applied voltagedifference of the pixel increases. Therefore, the effect of thehorizontal electric field increases, disclination occurs strongly, andimage quality is disturbed and is visually recognized.

On the other hand, disclination in a PWM driving scheme that expressesgradation with binary values ON/OFF will be described in detail withFIGS. 2A and 2B serving as examples. FIGS. 2A and 2B show gradationexpression in a liquid crystal panel employing a PWM driving scheme. Asshown in FIG. 2A, in this example, a period of one frame, which is atime period for expressing gradation, is divided into four subfields ofdifferent time periods, and by changing (or switching) ON/OFF of eachperiod, gradation is expressed with temporal integration. In a line witha gradation value of 0, a period during one frame is always an OFFperiod, and in a line with a gradation value of 15, a period during oneframe is always an ON period. In periods of gradation values 1 to 14,there are ON periods and OFF periods among subframe periods obtained bydividing the period of one frame. FIG. 2B shows, in the lines of FIG.2A, a projection image when an image is actually projected by the liquidcrystal panel, and here it is understood that a line having a gradationvalue of 0 represents black, a line having a gradation value of 15represents white, and lines having gradation values from 0 to 15represent gradations.

Here, when one of two adjacent pixels is ON while the other is OFF, ahorizontal electric field occurs, and in the ON pixel, a black region isformed in a part of a region adjacent to the adjacent OFF pixel, and asa result the illuminance of the ON pixel decreases. This is imagequality disturbance due to disclination. For example, in lines having agradation value of 7 and a gradation value of 8 in FIG. 2A, it isunderstood that in the entire period of one frame, one of these lines isON while the other is OFF. There is also a similar ON/OFF relationshipbetween the gradation 3 and the gradation 4, and between the gradation11 and the gradation 12, but in those cases the time period in which oneline is ON while the other line is OFF is shorter. Here, three blackstreaks are shown in FIG. 2B, and this indicates that in theabove-described three locations, the gradation is darker than theoriginal gradation due to disclination. Note that because the timeperiod of the two subfields in the first half of the frame are short,the effect of disclination is unlikely to be conspicuous. That is, it isnot the difference in gradation values between adjacent pixels, butrather, as the period during which the PWM pattern is ON/OFF betweenadjacent pixels increases, the degree of disturbance of disclinationincreases, that is, the degree of image quality deterioration increases.In other words, disclination is particularly likely to be visuallyrecognized in a gradation image with a small gradation differencebetween adjacent pixels.

Regarding this image quality disturbance due to disclinationcharacteristic to PWM driving, as described in Japanese Patent Laid-OpenNo. 2013-050679, a method is known in which correction values common toall pixels are added to gradation data, and the correction values aresuccessively (or periodically) changed for each frame so that theposition where disturbance occurs is moved at a time resolution thatcannot be visually recognized.

However, in multi-projection, particularly when gradation processing byedge blending has been performed, there is a problem that disturbancedue to disclination becomes easily visually recognized in an overlappingregion.

FIGS. 7A and 7B show, when performing multi-projection, how disclinationbecomes easily visually recognized due to gradation processing in anoverlapping region where edge blending is performed. Here, a white imageis used for input. In FIG. 7A, a first projector projects a projector 1image projected to the left, a second projector projects a projector 2image projected to the right, and in an overlapping region, an imagethat has undergone gradation processing on an input video signal isprojected. In the projector 1 image on the left side by the firstprojector, gain from a left end of the image to a projector 1 imagecompositing start position is set to 1, gain at a projector 1 imagecompositing end position that is the right end of the image is set to 0,and the gain from the projector 1 image compositing start position tothe projector 1 image compositing end position is applied by linearinterpolation. Also in the projector 2 image on the right side by thesecond projector, gain is set to 0 at a projector 2 image compositingstart position and gain is set to 1 at a projector 2 image compositingend position, and the gain between those positions is applied by linearinterpolation. As shown in FIG. 7B, when the overlapping regions of theimages with each other are overlapped, when the size of the overlappingregions of the projector 1 image and the projector 2 image are the same,the gain of the gradation processing for each image at any position inthe overlapping regions is added and becomes 1. In other words, it ispossible to composite the projector 1 image and the projector 2 imagewithout a brightness level difference between the overlapping regions.

Here, when the gain is smoothly changed by the gradation processing inthe overlapping regions, as described with reference to FIGS. 2A and 2B,disclination occurs between certain gradations and is easily visuallyrecognized. In FIG. 7A, gradation in the gain where disclination occursis defined as a disclination occurrence gradation 1 and a disclinationoccurrence gradation 2. In the projector 1 image and the projector 2image, vertical streaks, which are image quality disturbances due todisclination at the positions of the disclination occurrence gradation 1and the disclination occurrence gradation 2, are shown. Here, when theoverlapping regions are overlapped as shown in FIG. 7B, two blackstreaks of image quality disturbances due to disclination occur in eachof the projector 1 image and the projector 2 image respectively, andremain occurring in the overlapping regions as a total of four blackstreaks.

The following three points are listed as main reasons that black streaksbecome easily visually recognized by this disclination.

The location of occurrence of image quality disturbance is fixed to apartial region, which is the overlapping region of the projectionscreen.

When projection images are multi-projected aligned horizontally, anoverlapping region at the center of the screen is a region of interestfor users.

Image quality disturbance occurs in an overlapping region even in thecase of a pattern in which image quality disturbance due to disclinationdoes not normally occur, for example such as in the case of a whitesolid image in which there is no gradation change.

In other words, in a multi-projection system configured with aprojection apparatus using a PWM driving scheme and having a liquidcrystal display element, there is the problem that edge blendingtechnology does not enable the joint between screens to beinconspicuous, which is the essential aim of that technology.

SUMMARY OF THE INVENTION

Consequently, the present invention aims to provide, in amulti-projection system employing a projection apparatus using a PWMdriving scheme and having a liquid crystal display element, a projectionapparatus that does not cause an image quality disturbance due todisclination in an edge blending region to be visually recognized.

In order to attain such an aim, the present invention has the followingconfiguration.

According to one aspect of the present invention, there is provided afirst projection apparatus that together with a second projectionapparatus configures a multi-projection system, the first projectionapparatus comprising: an edge blending unit configured to perform edgeblending processing on a region overlapping with a projection imageprojected by the second projection apparatus; a changing unit configuredto change image gain properties of the edge blending processing by theedge blending unit successively, the image gain properties beingprovided such that a sum of image gain of a projection image projectedby the first projection apparatus and image gain of a projection imageprojected by the second projection apparatus is constant throughout anentire image; and a synchronous control unit configured to performsynchronous control of changing of the image gain properties by thechanging unit, between the first projection apparatus and the secondprojection apparatus.

Also, according to a second aspect of the present invention, there isprovided a multi-projection system including a first projectionapparatus and a second projection apparatus, the first projectionapparatus and the second projection apparatus respectively comprising:an edge blending unit configured to perform edge blending processing onan overlapping region of a projection image; a changing unit configuredto successively change image gain properties of the edge blendingprocessing by the edge blending unit, the image gain properties beingprovided such that a sum of image gain of a projection image projectedby the first projection apparatus and image gain of a projection imageprojected by the second projection apparatus is constant throughout anentire image; and a synchronous control unit configured to performsynchronous control of changing (switching) of the image gain propertiesby the changing unit, between the first projection apparatus and thesecond projection apparatus; wherein the changing unit of the firstprojection apparatus uses image gain properties for a master projectionapparatus, the synchronous control unit of the first projectionapparatus outputs, to the second projection apparatus, a synchronizationsignal for changing the image gain properties, the changing unit of thesecond projection apparatus uses image gain properties for a slaveprojection apparatus, and the synchronous control unit of the secondprojection apparatus changes the image gain properties synchronouslywith a synchronization signal that can be input from the firstprojection apparatus.

According to the present invention, in a multi-projection systememploying a projection apparatus using a PWM driving scheme and having aliquid crystal display element, it is possible to reduce imagedegradation due to disclination in an edge blending region, and obtain agood image.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the overall configuration of a front projector of thepresent embodiment.

FIG. 2A shows expression of gradation in a liquid crystal panelemploying PWM driving.

FIG. 2B shows expression of gradation in a liquid crystal panelemploying PWM driving.

FIG. 3 is a flowchart of the present embodiment.

FIG. 4A shows edge blending in multi-projection by two projectors.

FIG. 4B shows edge blending in multi-projection by two projectors.

FIG. 5A shows overlapping regions and compositing regions of the presentinvention.

FIG. 5B shows overlapping regions and compositing regions of the presentinvention.

FIG. 5C shows overlapping regions and compositing regions of the presentinvention.

FIG. 5D shows overlapping regions and compositing regions of the presentinvention.

FIG. 6A shows an example regarding FIG. 5B where specific numericalvalues are additionally used.

FIG. 6B shows an example regarding FIG. 5C where specific numericalvalues are additionally used.

FIG. 6C shows an example regarding FIG. 5D where specific numericalvalues are additionally used.

FIG. 7A shows how disclination becomes easily visually recognized due togradation processing in an overlapping region.

FIG. 7B shows how disclination becomes easily visually recognized due togradation processing in an overlapping region.

FIG. 8 illustrates a relationship between an edge blendingsynchronization signal and a set of correction values.

FIG. 9A illustrates a compositing region gain curve.

FIG. 9B illustrates a compositing region gain curve.

FIG. 9C illustrates a compositing region gain curve.

FIG. 9D illustrates a compositing region gain curve.

FIG. 10 is a block diagram of the present invention.

FIG. 11 illustrates multi-projection by two projectors.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

Overall Configuration

FIG. 11 illustrates a multi-projection system employing two projectors,i.e., projection apparatuses. Here, a first front projector 100 projectsa projector image 301, and a second front projector 200 projects aprojector image 302, onto a screen. The two projector images overlap inan overlapping region 303 and are projected so as to be synchronizedwith each other. These two front projectors each have the configurationshown in FIG. 1. In this example, video data (or a video signal) thateach projector projects, including the overlapping region, is input toeach projector.

Next is a description of the overall configuration of a front projectorof the present embodiment, with reference to FIG. 1.

FIG. 1 shows the overall configuration of the front projector 100 of thepresent embodiment.

The front projector 100 of the present embodiment has a CPU 110, a ROM111, a RAM 112, an operation unit 113, an image input unit 130, and aprojection image processing unit 140. The front projector 100additionally has a liquid crystal control unit 150, liquid crystalelements (liquid crystal panels) 151R, 151G, and 151B, a light sourcecontrol unit 160, a light source 161, a color separation unit 162, acolor compositing unit 163, an optical system control unit 170, aprojection optical system 171, a communications unit 180, a displaycontrol unit 195, a display unit 196, and an internal bus 199 connectingthese functional blocks.

The projector 100 additionally has an edge blending coefficientgeneration unit 181 and an edge blending synchronization unit 182.

The CPU 110 controls each operation block of the front projector 100,the ROM 111 stores a control program describing a processing procedureof the CPU 110, and the RAM 112 serves as a work memory that temporarilystores a control program or data. Also, the CPU 110 temporarily storesstill image data or moving image data that was received from the imageinput unit 130 or the communications unit 180, and by using a programstored in the ROM 111, also can reproduce respective images or video.

The operation unit 113 receives an instruction from a user and transmitsan instruction signal to the CPU 110, and is configured with, forexample, a switch, a dial, a touch panel provided on the display unit196, or the like. Also, the operation unit 113 may be, for example, asignal receiving unit (such as an infrared receiving unit) that receivesa signal from a remote control, and may be configured to transmit apredetermined instruction signal to the CPU 110 based on the receivedsignal. Also, the CPU 110 receives a control signal that was input fromthe operation unit 113 or the communication unit 180, and controls eachoperation block of the front projector 100.

The projection image processing unit 140 performs change processing onthe video signal received from the image input unit 130 to change aframe quantity, a pixel quantity, an image shape, or the like, andtransmits the processed video signal to the liquid crystal control unit150, and is configured with an image processing microprocessor or thelike. The projection image processing unit 140 is not required to be adedicated microprocessor, and for example, the CPU 110 may executesimilar processing as the projection image processing unit 140 accordingto a program stored in the ROM 111. The projection image processing unit140 can execute functions such as frame thinning processing, frameinterpolation processing, resolution conversion (scaling) processing,and distortion correction processing (keystone correction processing).Also, in addition to a video signal that was received from the videoinput unit 130, the projection image processing unit 140 can also applythe above-described change processing to an image or video that has beenreproduced by the CPU 110.

The liquid crystal control unit 150 controls a time period for applyinga voltage to liquid crystals of pixels of the liquid crystal elements151R, 151G, and 151B based on a video signal that has been processed bythe projection image processing unit 140, and adjusts the time period oftransmittance of the liquid crystal elements 151R, 151G, and 151B. Thisadjustment is as described with reference to FIGS. 2A and 2B. In otherwords, the liquid crystal control unit 150 is a driving circuit thatperforms PWM control of the liquid crystal elements. The liquid crystalelement 151R is a liquid crystal element corresponding to the color red,and of light that has been output from the light source 161, among lightthat has been separated into the colors red (R), green (G), and blue (B)by the color separation unit 162, is configured to adjust thetransmittance of light of the color red. The liquid crystal element 151Gis a liquid crystal element corresponding to the color green, and oflight that has been output from the light source 161, among light thathas been separated into the colors red (R), green (G), and blue (B) bythe color separation unit 162, is configured to adjust the transmittanceof light of the color green. The liquid crystal element 151B is a liquidcrystal element corresponding to the color blue, and of light that hasbeen output from the light source 161, among light that has beenseparated into the colors red (R), green (G), and blue (B) by the colorseparation unit 162, is configured to adjust the transmittance of lightof the color blue. An image corresponding to an image signal isoptically reproduced by the liquid crystal elements.

The light source control unit 160 controls ON/OFF of the light source161 and controls the light amount, and is configured with a controlmicroprocessor. The light source control unit 160 is not required to bea dedicated microprocessor, and for example, the CPU 110 may executesimilar processing as the light source control unit 160 according to aprogram stored in the ROM 111. The light source 161 outputs light forprojecting an image on an unshown screen, and may be a halogen lamp, axenon lamp, a high pressure mercury lamp, or the like, for example. Thecolor separation unit 162 separates the light that has been output fromthe light source 161 into the colors red (R), green (G), and blue (B),and is configured with a dichroic mirror, a prism, or the like, forexample. Note that when LEDs or the like corresponding to each color areused as the light source 161, the color separation unit 162 isunnecessary. The color compositing unit 163 composites light of thecolors red (R), green (G), and blue (B) transmitted through the liquidcrystal elements 151R, 151G, and 151B, and is configured with a dichroicmirror, a prism, or the like, for example. Then, light in which thecolors red (R), green (G), and blue (B) have been composited by thecolor compositing unit 163 is sent to the projection optical system 171.At this time, the liquid crystal elements 151R, 151G, and 151B arecontrolled by the liquid crystal control unit 150 such that there istransmittance of light corresponding to the image that was input fromthe projection image processing unit 140. Therefore, when the light thathas been composited by the color compositing unit 163 is projected onthe screen by the projection optical system 171, an image correspondingto the image that has been input by the projection image processing unit140 is displayed on the screen.

The optical system control unit 170 controls the projection opticalsystem 171, and is configured with a control microprocessor. The opticalsystem control unit 170 is not required to be a dedicatedmicroprocessor, and for example, the CPU 110 may execute similarprocessing as the optical system control unit 170 according to a programstored in the ROM 111. The projection optical system 171 projectscomposited light that has been output from the color compositing unit163 onto a screen, and is configured with a plurality of lenses and lensdriving actuators, and by driving the lenses with the actuators, it ispossible to perform enlargement, reduction, focus adjustment, or thelike of a projection image.

The communications unit 180 receives a control signal, still image data,moving image data, or the like from an external device, and thecommunications scheme is not particularly limited. For example, awireless LAN, a wired LAN, USB, Bluetooth (registered trademark), or thelike may be used. Further, if a terminal of the image input unit 130 is,for example, an HDMI (registered trademark) terminal, CEC communicationsmay be performed through that terminal. Here, as long as it is possibleto perform communications with the front projector 100, the externaldevice may be any sort of device such as a personal computer, a camera,a mobile phone, a smartphone, a hard disk recorder, a game machine, aremote control, or the like. In addition, in the present embodiment, theexternal device may be another front projector 100 for performingmulti-projection. In this case, through the communications unit 180, itis possible to transmit a corrected synchronization signal or the likedescribed later from one projector to another projector, or from anunshown control device to two projectors. In this configuration, imagesignal input may be performed using the image input unit 130.

The display control unit 195 performs control to display an image suchas an operation screen for operating the front projector 100 or an imagesuch as a switch icon in the display unit 196 provided in the frontprojector 100, and is configured with a microprocessor or the like thatperforms display control. A dedicated microprocessor for the displaycontrol unit 195 is not required, and for example, the CPU 110 mayexecute similar processing as the display control unit 195 according toa program stored in the ROM 111. Also, the display unit 196 displays anoperation screen and a switch icon for operating the front projector100. As long as the display unit 196 can display an image, anyconfiguration may be adopted for the display unit 196. For example, thedisplay unit 196 may be a liquid crystal display, a CRT display, anorganic EL display, or an LED display. Also, in order to present aspecific button in a recognizable manner to the user, LEDs or the likecorresponding to respective buttons may be caused to emit light.

Note that the projection image processing unit 140, the liquid crystalcontrol unit 150, the light source control unit 160, the optical systemcontrol unit 170, and the display control unit 195 of the presentembodiment may be a single microprocessor or a plurality ofmicroprocessors capable of performing similarly processing as each ofthese blocks. Also, for example, the CPU 110 may execute similarprocessing as each block according to a program stored in the ROM 111.Note that the video signal to be projected by each projector is dividedfor each projector when the video signal is input. The video signal, forexample, is digital data that has been divided into frames by a verticalsynchronization signal and divided into lines by a horizontalsynchronization signal, and is stored in a frame buffer secured in theRAM 112, for example. A plurality of frame buffers may be prepared asnecessary. Edge blending processing is performed on image data that hasbeen stored in the frame buffers, for example.

Projection Control Processing

FIG. 10 is a block diagram centered on the projection image processingunit 140 shown in FIG. 1. The projection image processing unit 140includes an edge blending unit 1401. In the first projector 100 and thesecond projector 200, images obtained by dividing an original image foreach projector to project, and respectively including an overlappingregion 303, are input from the image input unit 130 of each projector.Also, the two projectors are configured to be connected through thecommunications unit 180 of each projector.

FIG. 3 is a flow chart of the present embodiment, and shows a procedureexecutable by the projection image processing unit 140 of each of thefirst projector 100 and the second projector 200. Note that thisprocedure may also be executed by the CPU 110 rather than the projectionimage processing unit 140.

Step S301 is the start of image correction processing in the presentembodiment. For example, execution is started from step S301 after powerof the projector is turned on and initialization processing and the likehave been completed. In step S302, it is determined whether or not thereis a request to perform multi-projection by a plurality of projectorsincluding the projector itself performing processing. Requests of aplurality of projectors are generated, for example, by an instructionfrom an unshown computer or by a switch operation provided in theoperation unit 113, and occurrence of such a request can be detected by,for example, an interruption or a test of a value of a predeterminedstorage region. If there is no request for a plurality of projectors,the procedure returns to step S302. If there is a request for aplurality of projectors, the procedure moves to step S303 and requestssetting of the projection conditions.

In step S303, projection conditions are requested. The projectionconditions include projector arrangement/projection information such as,for example, the following sort of conditions.

(1) How many projectors are used to configure a projection image? Inother words, the quantity of projectors that project one image that hasbeen divided.

(2) Which projector projects which region of a composited projectionimage. In other words, assignment of an image region to a projector.

(3) In a projection image of a projector, which edge is set for edgeblending. In other words, the edge of a screen to set for edge blending.

(4) The position of the overlapping region where projection imagesoverlap, and the address of the compositing region to be subjected toedge blending processing.

(5) Shape of a gain curve in the compositing region of the projectionimage. In other words, properties of image gain in the compositingregion. The image gain properties can be provided by, for example, acoefficient table, a function, or the like.

Note that in this example, the video signal to be input to eachprojector has already been divided, so if each projector knows at leastthe projection conditions (4) and (5), projection of the assignmentregion and necessary edge blending can be performed. Note that aconfiguration can also be adopted in which a video signal beforedivision is input to each projector, the region to be projected isextracted from that video signal by each projector, and each projectorprojects the extracted region. In that case, condition (2) is alsorequired for frame extraction.

Here, FIGS. 4A and 4B show the overlapping region 303 and imagecompositing when performing multi-projection by the first projector 100and the second projector 200, and projection condition will be describedwith reference to these drawings. FIG. 4A shows the projection positionof each projection image on the projection plane and the gain in gaincontrol to the projection image of each projector in the overlappingregion 303 of the projection images. This shows multi-projection beingperformed with two projectors, the first projector 100 and the secondprojector 200. Also, this shows that the first projector 100 projectsthe image on the left side of the multi-projection image and the secondprojector 200 projects the image on the right side. Because the firstprojector 100 projects the image on the left side, for this projectorthe overlapping region is set to the edge on the right side. Also,because the second projector 200 projects the image on the right side,for this projector the overlapping region is set to the edge on the leftside. Here, the overlapping region 303 is defined as a region whereprojection images of each projector are overlapped in order to performmulti-projection. Also, a compositing region is defined as a regionwhere gain of respective projection images is controlled in order tosmoothly perform compositing of projection images with each other. Inorder to smoothly composite images with each other in the compositingregion, in this example from left to right, projector 1 image gain iscontrolled from 1 to 0 and projector 2 image gain is controlled from 0to 1. In other words, in the compositing region, the image gain on theside of the edge of the image to be projected is 0, and the image gainon the other side is a value equal to the image gain of the image exceptfor the compositing region, i.e., a value of 1. By performing controlsuch that in any position, summing the projector 1 image gain and theprojector 2 image gain results in a value of 1, images can be compositedsmoothly without causing a brightness level difference to occur.Commonly, in multi-projection, the overlapping region 303 where theprojector 1 image and the projector 2 image overlap is the compositingregion for smoothly compositing the images.

FIG. 4B shows images of the first projector 100 and the second projector200 respectively, on which independent gain control has been performed,and image gain properties. Here, in the projector 1 image gain, the gainis 1 at the projector 1 compositing start address, the gain is 0 at theprojector 1 compositing end address, and the gain therebetween is set tobe linear. Also in the projector 2 image gain, the gain is 0 at theprojector 2 compositing start address, the gain is 1 at the projector 2compositing end address, and the gain therebetween is set to be linear.Here, the image gain properties in the compositing region are linearwith respect to the position in the horizontal direction. However, theimage gain properties in the compositing region are not limited to beinglinear, and as described with reference to FIG. 4A, as long as summingthe projector 1 image gain and the projector 2 image gain at anyposition results in a value of 1, properties such as those of aquadratic curve, a cubic curve, or the like may be used.

In step S304, it is determined whether or not the setting values of theprojection conditions have been input to the corresponding projector.The projection conditions subject to the determination include at leastconditions that can specify the region assigned to each projector andthe parameters of edge blending, for example such as the conditions (4)and (5). If such projection conditions have not been input, theprocedure returns to step S303. If input has completed, the procedureproceeds to step S305.

In step S305, input of the settings values of the projection conditionsfor multi-projection has already been completed in the projectors(abbreviated as PJ in FIG. 3), so projection images where gain controlreflecting the settings values has been performed are projected from theprojectors. While measuring and observing these projection images, theoperator performs position matching of the projection images of the twoprojectors here. Here, as shown in FIG. 4A, the operator controlszooming, optical shift, setting position, and the like of the opticalsystem such that the positions of the compositing start address and thecompositing end address of each projection image by the first projector100 and the second projector 200 overlap, thus matching the positions ofthe projection images. When doing so, in the first projector 100 and thesecond projector 200, position matching by the operator may be assistedby outputting a marker image at the positions of the compositing startaddress and the compositing end address of the video signal to beprojected.

In step S306, it is determined whether or not the correspondingprojector has been designated as the master projector from the operator.If the corresponding projector has been designated as the masterprojector, the procedure moves to step S307, and if the correspondingprojector has not been specified as the master projector, the proceduremoves to step S308. For example, one of two projectors that project twoframes sharing one overlapping region in a certain direction isspecified as a master projector, i.e., a master projection apparatus,and the other is a slave projector, i.e., a slave projection apparatus.The designation of the master projector may, for example, be performedexplicitly by operation of the operation unit 113, or for example, aprojector or the like to which a specific region has been assigned mayimplicitly be the master projector. Note that in a case where eachregion obtained by dividing the original image into the verticaldirection and the horizontal direction has been assigned to a pluralityof projectors, it is possible that overlapping regions overlap eachother, and four overlapping regions overlap at the corner of a frame. Inthis case as well, edge blending processing may be performed on oneoverlapping region with the master projector and the slave projectorrelated to that overlapping region in synchronization, and may beperformed independently from processing of another overlapping regionthat overlaps. In this case, one projector can serve as the master withrespect to one overlapping region and as the slave with respect to theother overlapping region.

Step S307 is stated for a case where, in step S306, the first projector100 that is the projector of the present description serves as themaster projector and the second projector 200 that is another projectorserves as the slave projector. In the first projector 100 that is themaster projector, correction information for the master projector thatis stored in advance in the ROM 111 is selected in the edge blendingcoefficient generation unit 181. This correction information may beprepared in advance and stored in the ROM 111, or may be generated whenthere is a request for multi-projection of the present invention andstored in the RAM 112. Also, correction information may be generated inreal-time at the time of projection.

Description of Correction Information

Corrections allowing degradation of image quality due to disclination inan embodiment of the present invention to be less visible, andcorrection information to accomplish this, will be described withreference to FIGS. 5A to 5D. FIG. 5A shows projection images when thefirst projector 100 and the second projector 200 are installed and setby the operator in step S305. Here,

the overlapping start address of the first projector 100 is representedby A1_lapstart,

the overlapping end address of the first projector 100 is represented byA1_lapend,

the overlapping start address of the second projector 200 is representedby A2_lapstart,

the overlapping end address of the second projector 200 is representedby A2_lapend,

the size of the overlapping region is represented by Dlap,

the horizontal length of the liquid crystal panel of the first projector100 is represented by DevRes 1, and

the horizontal length of the liquid crystal panel of the secondprojector 200 is represented by DevRes 2.

Note that in this example, both the size and the address are in units ofpixels. The address stated here is assumed to be an address of the framebuffer of each projector. Also, the address is a value focused only onthe component in the direction of lining up the overlapping regions (thehorizontal direction of the frames in FIGS. 5A to 5D). Therefore, if theregions are lined up vertically, this is a vertical direction component.In FIG. 5A, these values are already decided (set) in steps S303 andS304 at the time of installation and setting by the operator in stepS305, or alternatively are fixed values.

FIGS. 5B, 5C, and 5D show compositing regions and compositing addressesof the first projector 100 and the second projector 200. Here,

the compositing start address of the first projector 100 is representedby A1_synthstart,

the compositing end address of the first projector 100 is represented byA1_synthend,

the compositing start address of the second projector 200 is representedby A2_synthstart,

-   -   the compositing end address of the second projector 200 is        represented by A2_synthend, and        the size of the compositing region is represented by Dsynth.

These values also are set in steps S303 and S304, or alternatively areprovided as fixed values. However, as described later, the compositingstart address and the compositing end address are not fixed to a singlevalue, but take values corresponding to each of a plurality of sets.Accordingly, addresses provided as fixed values are also differentaddresses for each of a plurality of sets. Also, in this example, evenif the compositing start address and the compositing end address change,an expression of compositing end address−compositing startaddress=“width of the compositing region” is set to a constant value,but this does not necessarily have to be a constant value.

The present embodiment is characterized by differing from theconventional edge blending processing when performing multi-projectionin which image degradation due to disclination is not considered, inthat the compositing region is narrower than the overlapping region andhas a plurality of compositing start addresses and compositing endaddresses as correction values, and the image gain propertiescorresponding to those correction values are successively changed (orperiodically switched), for example, for each frame.

FIGS. 5B, 5C, and 5D each show a combination of a compositing startaddress and a compositing end address in which the compositing regionDsynth position differs within the range of the overlapping region Dlap.In this example, the compositing start address and the compositing endaddress each belong to three sets, and each set is applied by changing(or switching) the set for each frame. However, even if the compositingregion Dsynth position of the projection images of the first projector100 and the second projector 200 changes, the compositing image that isultimately projected, shown in FIG. 5A, does not change.

FIGS. 6A to 6C illustrate a case regarding FIGS. 5A to 5D where specificnumerical values are additionally used. The overlapping region Dlap andthe compositing region Dsynth are known numerical values set in advanceby the operator, and here the overlapping region Dlap=480 and thecompositing region Dsynth=360. In multi-projection, the narrower theoverlapping region Dlap, the greater the size of compositing image thatcan be projected. However, the overlapping region Dlap is a region forsmoothly compositing the adjacent images with each other, and when theoverlapping region Dlap is too narrow, the influence on the boundarywith the adjacent image due to shaking of the projection image caused byshaking or vibration of the installed projector becomes relativelylarge, and so the boundary becomes easy to see. Therefore, the size ofthe overlapping region Dlap is decided (set) in consideration of thestability of the position where the projector is installed, and changesin that position over time. Commonly, the overlapping region Dlap isoften set to about 10% to 30% of a length DevRes in the horizontaldirection of the frame buffer. In the present embodiment, as an example,the length DevRes is set to 1920, and the overlapping region Dlap is setto 480, which is 25% of the length DevRes. Also, the compositing regionDsynth is set smaller than the overlapping region Dlap. Here, thecompositing region Dsynth is set to 360, which is a size that is 75% ofthe overlapping region Dlap. In the present embodiment, the number ofpixels in the horizontal direction of the liquid crystal panel isdescribed as a resolution DevRes1=DevRes2=1920, which is the same as thelength in the horizontal direction of the frame buffer for anyprojector.

Because the overlapping region Dlap, the compositing region Dsynth, andthe projection position are already known, the projector 1 overlappingstart address A1_lapstart, the projector 1 overlapping end addressA1_lapend, the projector 2 overlapping start address A2_lapstart, andthe projector 2 overlapping end address A2_lapend can be uniquelydecided (set) from the following Expressions 1 to 4.A1_lapstart=DevRes1−Dlap  (Expression 1)A1_lapend=DevRes1−1  (Expression 2)A2_lapstart=0  (Expression 3)A2_lapend=Dlap−1  (Expression 4)According to the numerical values calculated here, as described above,in step S305 the operator installs and sets the first projector 100 andthe second projector 200. Then, regarding the projector 1 compositingstart address A1_synthstart, the projector 1 compositing end addressA1_synthend, the projector 2 compositing start address A2_synthstart,and the projector 2 compositing end address A2_synthend, which are thecorrection values of the present embodiment, if one of these fourparameters has been determined, the other three parameters can beuniquely decided (set) according to the value of Dsynth. Calculation ofthe following correction values may be calculated in advance by theoperator or may be calculated by the CPU 110.

First, the compositing start address A1_synthstart of the firstprojector 100 is decided (set) within the conditions of the followingExpression 5.A1_lapstart≤A1_synthstart≤(A1_lapend−Dsynth)  (Expression 5)At this time, as a method of deciding (setting) the projector 1compositing start address A1_synthstart, for example, numerical valuesprepared in advance may be used, or this parameter may be determinedusing random numbers. If the projector 1 compositing start addressA1_synthstart has been determined, the remaining values are calculatedfrom the following Expressions 6 to 8.A1_synthend=A1_synthstart+Dsynth−1  (Expression 6)A2_synthstart=A1_synthstart−A1_lapstart  (Expression 7)A2_synthend=A2_synthstart+Dsynth−1  (Expression 8).

An example of each setting value including specific numerical values isshown in FIGS. 6A to 6C. In FIGS. 6A to 6C, as described above, thehorizontal resolutions DevRes1 and DevRes2 of the panel are 1920 and thehorizontal resolution of the overlapping region Dlap is 480. That is, inFIG. 5A, the horizontal resolutions of the image of the first projector100 and the image of the projector 2 are 1920, the horizontal resolutionof the overlapping region is 480, and the horizontal resolution of theprojection compositing image is 3360, calculated from (DevRes×2−Dlap).FIG. 6A shows a specific example corresponding to FIG. 5B, FIG. 6B showsa specific example corresponding to FIG. 5C, and FIG. 6C shows aspecific example corresponding to FIG. 5D. As described above, in thisway a plurality of correction values for the first projector 100 and thesecond projector 200 including the compositing start address and thecompositing end address are generated as one set. This may be calculatedusing a PC (Personal Computer) or the like, or may be calculated by theedge blending coefficient generation unit 181.

That is, in FIG. 6A,

Projector 1 compositing start address A1_synthstart=1500

Projector 1 compositing end address A1_synthend=1859

Projector 2 compositing start address A2_synthstart=60

Projector 2 compositing end address A2_synthend=419 in FIG. 6B,

Projector 1 compositing start address A1_synthstart=1440

Projector 1 compositing end address A1_synthend=1799

Projector 2 compositing start address A2_synthstart=0

Projector 2 compositing end address A2_synthend=359 and in FIG. 6C,

Projector 1 compositing start address A1_synthstart=1560

Projector 1 compositing end address A1_synthend=1919

Projector 2 compositing start address A2_synthstart=120

Projector 2 compositing end address A2_synthend=479.

Although generation of three correction value sets in FIGS. 6A to 6C hasbeen described, the quantity of correction value sets may be three ormore.

The correction values generated in this way may be stored in advance inthe ROM 111, or may be generated and stored in the RAM 112 when there isa request for projection by a plurality of projectors according to thepresent invention. These items of correction information may becalculated by the first projector 100 serving as the master projectorand distributed to the second projector 200 through the communicationsunit 180, or may be calculated in advance using an unshown externaldevice such as a PC connected to the communication unit 180, anddistributed to the first projector 100 and the second projector 200.

Continued Description of FIG. 3

In step S307, among the correction values that have been thus generatedand stored in the ROM 111 or the RAM 112, a correction value set for themaster projector is selected. That is, the projector 1 compositing startaddress A1_synthstart and the projector 1 compositing end addressA1_synthend are selected. In step S308, among the correction values thathave been generated as described in step S307 and stored in the ROM 111or RAM 112 in advance, a correction value set for the slave projector isselected. That is, the projector 2 compositing start addressA2_synthstart and the projector 2 compositing end address A2_synthendare selected. In step S309, the master projector generates an edgeblending synchronization signal, which is a reference timing in the edgeblending synchronization unit 182, and transmits this signal to thesecond projector 200 serving as a slave projector through thecommunication unit 180 of the master projector. Here, the edge blendingsynchronization signal indicates a combination of correction values tobe applied to the image that each projector projects. In step S310, whenthe projector performing the procedure is a slave projector, thisprojector receives the edge blending synchronization signal from themaster projector through this slave projector's own communications unit180. Here, this projector serves as the second projector 200.

In step S311, in the first projector 100 serving as the masterprojector, based on the edge blending synchronization signal generatedby the edge blending synchronization unit 182, the correction valuesstored in the ROM 111 or the RAM 112 of this projector are changed (orswitched) for each frame. In the second projector 200 serving as theslave projector, based on the edge blending synchronization signalreceived from the first projector 100 serving as the master projectorthrough the communications unit 180, the correction values stored in theROM 111 or the RAM 112 of this projector are changed (or switched) foreach frame. For example, when three sets of correction values have beengenerated as described with reference to FIGS. 5B, 5C, and 5D, in thefirst projector 100 serving as the master projector and the secondprojector 200 serving as the slave projector, correction values arechanged (or switched) among these three sets in accordance with the edgeblending synchronization signals. For example, a frame number isassigned beginning from 0, the frame number is grouped by remainder withthe quantity of sets of correction values as divisor, and edge blendingis performed using the same set of correction values for each group. Forexample, if there are three sets of correction values as in FIGS. 5B,5C, and 5D, the remainder is some number among 0, 1, and 2. If framesbelonging to groups having remainders of 0, 1, and 2 are respectivelycalled frames n, n+1, and n+2, for example, the correction value set inFIG. 5B is changed (or switched) in frame n, the correction value set inFIG. 5C is changed (or switched) in frame n+1, the correction value setin FIG. 5D is changed (or switched) in frame n+2, and for subsequentframes, respective correction values are changed (or switched) whilerepeating these.

In step S312, edge blending processing is performed on the input videosignal in the edge blending unit 1401 based on the correction valuesthat have been changing (or switched) for each frame in S311. Here, theedge blending processing is processing to perform gain processing on theinput image based on the compositing start address and the compositingend address, which are the correction values that have been changing (orswitched) for each frame in step S311. In the gain processing, asdescribed above, the master projector and the slave projectorrespectively apply the given gain properties to a section of image datafrom the compositing start address to the compositing end address, whichcan be designated with the set of correction values that were decided(set) in step S311. Note that for regions other than the compositingregion, by setting the gain to 1, gain can be applied to all of theimage data in a frame.

Synchronization of Correction Processing

FIG. 8 illustrates the relationship between the edge blendingsynchronization signals and the correction value sets. Operation fromstep S307 to step S312 will be described with reference to this drawing.Video signals to be projected by the first projector 100 and the secondprojector 200 are input to the projectors from the image input unit 130.The edge blending synchronization unit 182 of the first projector 100and the second projector 200 generates an edge blending synchronizationsignal from a Vsync signal that has been input. The edge blendingsynchronization signal is a signal indicating which combination toselect among the correction value sets stored in the ROM 111 or the RAM112.

In frame n, the edge blending synchronization signal indicates acorrection value 01. Then, in the first projector 100 serving as themaster projector, in the edge blending coefficient generation unit 181,the correction value 01 for the first projector 100 is read from the ROM111 or the RAM 112. Because one set of correction values includes valuesfor a master and a slave, each projector reads a correction valueaccording to its role. The first projector 100 is the master, so thisprojector reads the correction value of the master projector. Then, thatcorrection value is set in the edge blending unit 1401. According to thecorrection value that has been set in the edge blending unit 1401, gain(i.e., the correction value for the pixel value) is applied according tothe gain properties for the video signal that has been input.Specifically, here, the correction value is the projector 1 compositingstart address A1_synthstart and the projector 1 compositing end addressA1_synthend, and until the address of the input video signal changesfrom the projector 1 compositing start address A1_synthstart to theprojector 1 compositing end address A1_synthend, gain control isperformed on the input video signal according to the predetermined gainproperties as indicated by the projector 1 image in FIG. 6A. Note thatin this example, because the gain properties are linear, it is possibleto decide (set) the gain by linearly interpolating the gain for pixelsat each address from the compositing start address and the compositingend address. Therefore, although the compositing start address and thecompositing end address are called correction values, if the gain is notlinear, the correction values can include gain properties in addition toan address indicating the compositing region.

In the second projector 200 serving as the slave projector, the edgeblending synchronization signal generated by the edge blendingsynchronization unit 182 of the first projector 100 is received with thecommunication unit 180 of the second projector 200 through thecommunications unit 180 of the projector 1 and a communications cable400. The edge blending synchronization signal received with thecommunications unit 180 of the second projector 200, in the edgeblending coefficient generation unit 181 of the second projector 200,reads the correction values for the second projector 200 from the ROM111 or the RAM 112. The second projector 200 is the slave, so thisprojector reads the correction value of the slave projector. Then, thatcorrection value is set to the edge blending unit 1401 of the secondprojector 200. Gain is applied to the video signal that has been inputaccording to the correction values that have been set in the edgeblending unit 1401. Specifically, here, the correction value is theprojector 2 compositing start address A2_synthstart and the projector 2compositing end address A2_synthend, and until the address of the inputvideo signal changes from the projector 2 compositing start addressA2_synthstart to the projector 2 compositing end address A2_synthend,gain control is performed on the input video signal as indicated by theprojector 2 image in FIG. 6A.

In the frame n+1 that is the next frame, similarly, the correction value02 is applied to each projector. That is, the gain properties shown inFIG. 6B are applied to the frame. In the frame n+2 that follows, thecorrection value 03 is applied. That is, the gain properties shown inFIG. 6C are applied to the frame. Subsequently, correction values areselected and applied according to the edge blending synchronizationsignal. When the edge blending synchronization signal repeats in a 3frame period, FIGS. 6A to 6C are repeated in a 3 frame period.

In step S313, it is confirmed whether to end projection by a pluralityof projectors. If not ending projection, the procedure returns to stepS311. If ending projection, the procedure moves to step S314. In stepS314, processing is ended.

As stated above, in the present embodiment, in the overlapping region ofprojection images in multi-projection, each projector sharing theoverlapping region synchronizes and applies different compositingaddresses for each frame. Thus, the compositing regions are allowed tochange position in the spatial direction of the projection screens. As aresult, the position where image disturbance occurs due to disclinationcaused by PWM driving of the liquid crystal panels is moved for eachframe, and so a good image is obtained in which image disturbance isdifficult to see.

Also, instead of changing the gain properties for each frame, the gainproperties may be changed at an interval of a fixed quantity of frames.Also, image gain may be constant throughout an entire image projected bythe multi-projection system. In the above example, gain is controlledwith respect to both compositing regions and other regions so that gainis 1 throughout the entire image. However, even if gain is a value otherthan 1, if the gain is constant, the boundary of images betweenprojectors can be made inconspicuous, and disclination can be prevented.

Second Embodiment

In the first embodiment, as the correction values, the compositing startaddress and the compositing end address are changed (or switched) foreach frame, but a configuration may also be adopted in which, other thanthose addresses, the gain properties in the compositing region aredifferent for each frame.

FIGS. 9A to 9D illustrate gain properties of the compositing region.Here, FIG. 9A shows a state of the projection image of the firstprojector 100 and the projection image of the second projector 200overlapping each other. FIGS. 9B, 9C and 9D show the gain properties inrespective frames. In the above description of the first embodiment, thecorrection values are the compositing start address and the compositingend address, but here the correction value is the gain properties of thecompositing region. For gain properties in this compositing region, inFIGS. 9B, 9C, and 9D, in the compositing region of the projection imagesof the first projector 100 and the second projector 200, the summedvalue of the gain at the same position is 1 everywhere. These gainproperties can be stored in the ROM 111 or the RAM 112. Then, asdescribed in the above embodiment, the edge blending coefficientgeneration unit 181 selects the gain curve of FIG. 9B in frame n,selects the gain properties of FIG. 9C in frame n+1, and selects thegain properties of FIG. 9D in frame n+2, and sets them in the edgeblending unit 1401, and therefore the same effects as in the aboveembodiment can be obtained. In this case, particularly in the case ofFIGS. 9B and 9D, gain cannot be specified only by the start address andthe end address of the compositing region, so gain is provided as afunction or a table. Also, rather than applying each individually, aconfiguration may be adopted in which each of the compositing startaddress, the compositing end address, and the gain properties in theoverlapping region or the compositing region are combined as items thatare different for each frame, and applied in a combination.

As stated above, in the present embodiment, in the overlapping region ofprojection images in multi-projection, gain properties, which arecompositing ratios of projection images that differ for each frame, areapplied with each projection image synchronized. As a result, theposition where image disturbance occurs due to disclination caused byPWM driving of the liquid crystal panels is moved for each frame, and soa good image is obtained in which image disturbance is difficult to see.

Other Embodiments

In the above embodiment, an example is described in which two projectorsare disposed in the horizontal direction, and any of the left edge andthe right edge of a screen overlaps. Here, the overlapping portion mayspan a plurality of screen locations. For example, the inventionaccording to the present embodiment is also applicable to amulti-projection system having projectors disposed in two dimensions. Inthis case, at least any of the left edge and the right edge, and atleast any of the upper edge and the lower edge, of a screen projected bya certain projector overlap the screen of another projector. Theinvention according to the present embodiment may also be applied tothese overlapping portions. In this case, synchronous control isnecessary for the overlapping portions between two projectorssynchronizing gain properties, but synchronous control is not necessaryfor an image not synchronizing gain properties.

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-087384, filed Apr. 25, 2016 which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A first projection apparatus that together with asecond projection apparatus are projection apparatuses of amulti-projection system with edge blending processing, the firstprojection apparatus comprising: a projection unit configured to projectan image on a screen; at least one processor; and at least one memorystoring at least one program which, when executed by the at least oneprocessor, causes the first projection apparatus to: (1) acquire aninput image; (2) set an image gain curve for an overlapping region of aninput image, the image gain curve being used for overlapping, in theoverlapping region, a first image projected by the first projectionapparatus and a second image projected by the second projectionapparatus; and (3) control the projection unit to project an image basedon the input image in which the image gain curve is applied to theoverlapping region, wherein the image gain curve is changed at aninterval of a predetermined number of frames.
 2. The first projectionapparatus according to claim 1, wherein the image gain curve is changedsuch that at least one of (a) a position of a compositing region to besubjected to the edge blending processing, and (b) a shape of the imagegain curve, changes.
 3. The first projection apparatus according toclaim 2, wherein the position of the compositing region to be subjectedto the edge blending processing within the overlapping region ischanged, and wherein the image gain curve is a curve such that the imagegain at one edge of the compositing region is 0, and the image gain atanother edge is a value equal to the image gain of the projection imageother than in the compositing region, and the gain between the edges isprovided linearly according to the gain of the edges.
 4. The firstprojection apparatus according to claim 1, wherein the image gain curveis changed for each frame.
 5. The first projection apparatus accordingto claim 1, wherein the projection unit includes: a liquid crystalelement configured to optically reproduce an image according to theinput image; and a driving circuit configured to perform PWM control ofthe liquid crystal element.
 6. The first projection apparatus accordingto claim 1, wherein the first projection apparatus and the secondprojection apparatus change respective image gain curves synchronously.7. A multi-projection system with edge blending processing, the systemincluding a first projection apparatus and a second projectionapparatus, wherein each of the first projection apparatus and the secondprojection apparatus comprises: a projection unit configured to projectan image on a screen; at least one processor; and at least one memorystoring at least one program which, when executed by the at least oneprocessor, causes the projection apparatus to: (1) acquire an inputimage; (2) set an image gain curve for an overlapping region of theinput image, the image gain curve being used for overlapping, in theoverlapping region, a first image projected by the first projectionapparatus and a second image projected by the second projectionapparatus; and (3) control the projection unit to project an image basedon the input image to which the image gain curve is applied, wherein theimage gain curve is changed at an interval of a predetermined number offrames, and wherein the first projection apparatus and the secondprojection apparatus change respective image gain curves synchronously.8. A method of controlling a first projection apparatus that togetherwith a second projection apparatus are projection apparatuses of amulti-projection system with edge blending processing, wherein the firstprojection apparatus comprises a projection unit configured to projectan image on a screen, the method comprising: acquiring an input image;setting an image gain curve for an overlapping region of the inputimage, the image gain curve being used for overlapping, in theoverlapping region, a first image projected by the first projectionapparatus and a second image projected by the second projectionapparatus; outputting a synchronous signal which indicates the imagegain curve set by the setting; and controlling the projection unit toproject an image based on the input image to which the image gain curveis applied, wherein the image gain curve is changed at an interval of apredetermined number of frames.
 9. A non-transitory computer-readablemedium storing a program for, when executed, causing a computer,configured to control a first projection apparatus that together with asecond projection apparatus are projection apparatuses of amulti-projection system with edge blending processing, to perform amethod comprising: acquiring an input image; setting an image gain curvefor an overlapping region of the input image, the image gain curve beingused for overlapping, in the overlapping region, a first image projectedby the first projection apparatus and a second image projected by thesecond projection apparatus; and controlling a projection unit toproject an image on a screen based on the input image to which the imagegain curve is applied, wherein the image gain curve is changed at aninterval of a predetermined number of frames.
 10. The first projectionapparatus according to claim 1, wherein the at least one program, whenexecuted by the at least one processor, further causes the firstprojection apparatus to output a synchronous signal corresponding to theimage gain curve.